This invention relates to a filter and more particularly, but not exclusively, to a final stage filter for a fuel injection device.
Devices commonly known as xe2x80x9cedge filtersxe2x80x9d are typically disposed in a fuel injector or injector adapter to protect the finely dimensioned final stage conduits of an injection device, which may be as small as around 25 xcexcm in diameter, from contamination by undesirably large particles. Such particles may, for example, be the residue of the combustion process, internal deterioration debris, service-induced debris, or matter that has penetrated the main filter. A fuel injection device having an edge filter typically defines a narrow passageway between a surface of the edge filter and a housing of the device in which the edge filter is disposed, for removing particles above a predetermined size from fuel that must flow through the passageway towards an outlet of the injector.
The inventor has identified two main problems with such edge filters. Firstly, the housing that partially forms the passageway has been found to elastically extend so as to dilate away from the surface of the edge filter when subjected to fuel under high pressure, thereby temporarily widening the passageway and permitting oversize contaminant particles to pass. Secondly, an oversize particle is continually re-presented to the passageway""s entrance so that the particle is inevitably either reshaped by the high pressure fuel entering the passageway until it is small enough in at least one dimension to fit through the passageway, or the particle passes through the passageway as the wall of the injector dilates. These problems can lead to an edge filter passing contaminant particles having dimensions of significantly larger than the nominal spacing of the wall of the passageway from the surface of the edge filter.
An object of the invention is to mitigate or overcome at least one of the above-mentioned problems.
Accordingly, the invention provides a filter for a fuel injection device, comprising a plurality of filter elements arranged within a housing such that, in use, fluid is directed through clearances of predetermined size between respective mutually adjacent ones of the elements for preventing the passage of oversized contaminant particles carried in the fluid.
Preferably, the elements are arranged side by side in a loop such that, in use, force exerted on one side of one of the elements by pressurized fluid in a respective one of the clearances is opposed by force exerted on another side of this element by pressurized fluid in a next adjacent one of the clearances.
In this manner, the effects of high pressure in the filter clearances can be balanced and any significant increase in the size of the clearances due to the fuel pressure can be alleviated.
The invention also includes a fuel injection device having a housing, a 3 filter disposed in the housing for rejecting oversized contaminant particles, and a particle collection zone, the filter being configured and arranged relative to the housing such that, in use, fluid flowing through the filter directs rejected particles away from the filter into the particle collection zone.
This reduces time spent by a particle in contact with the filter, and reduces the opportunity for high-pressure pulses in the fluid to reshape the particle and force it through the filter.
The filter is conveniently of the type described hereinbefore.